The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Vehicle electronic control systems, such as engine control systems and transmission control systems, use electrical and electromechanical/hydraulic/pneumatic devices to monitor operating conditions and to adjust operation. As vehicle control systems have increased in size and complexity, the speed and precision for controlling and monitoring the devices has also increased. The vehicle control systems usually include diagnostic systems that determine whether the devices (e.g., devices generating input signals and output devices) are functioning as designed. Demands on the diagnostic systems have increased as the vehicle control systems have become more complex. A requirement of vehicle diagnostic systems may be quick and accurate detection of critical type faults, including both continuous and intermittent faults, in order to maintain reliable operation of the control system.
Functional performance requirements of a vehicle control system or a particular subsystem and its components may vary. For example, the diagnostic system may be required to detect and respond to an electrical fault of a first device or first input signal in less than 50 milliseconds to maintain and stabilize operation of the control system. Other input signals or output devices may allow diagnosis and response over longer or shorter intervals.
A diagnostic system may be designed to detect and respond to a continuous (non-intermittent) fault that is present for a predetermined period, such as 5 seconds or longer. When the fault is present for at least the predetermined period, the diagnostic system sets a Diagnostic Trouble Code (DTC) to inform the operator that a failure has occurred and that the vehicle requires service. When the DTC is set, the diagnostic system performs failure mode management action(s) to protect the system or subsystem. The failure mode management action(s) taken when the DTC is set is referred to as a permanent default action since the action(s) is/are performed as long as the DTC is set. A DTC is unique for each individual fault and is used to direct a vehicle service/repair to help efficiently identify the root cause of the failure. The DTC is also used to alert a user, via one or more tactile (e.g., visual, audio, etc.) indications that a fault has occurred and to seek vehicle service.
Requiring the fault to be continuous and present for longer periods of time (for example only, 5 to 10 seconds) allows the diagnostic system to reduce the likelihood that a false failure has occurred or that the fault is intermittent. False failures and intermittent faults may increase warranty costs and decrease customer satisfaction. A false failure may occur when the diagnostic system indicates that a fault is present when no actual fault is present and/or sets a DTC prematurely when the fault has been intermittent. Prematurely setting a DTC can limit operation of the vehicle control system and therefore cause customer inconvenience. Prematurely setting a DTC may also increase warranty costs because a vehicle service technician may be unable to identify the root cause of the fault.
Intermittent faults are transitory and can be short in duration, random, erratic, non-repeatable, and/or repeatable. Intermittent faults are now considered critical faults because they may be detrimental to proper operation of a complex control system. It is no longer a matter of preference as to whether a diagnostic system takes or does not take failure mode management action(s) in response to intermittent faults. Diagnostic systems must therefore identify and quantify intermittent faults with minimal (e.g., zero) delay or latency in order to take appropriate failure mode management action(s) at the ideal time.
Detection and quantification of intermittent faults can increase false passes and/or false failures. A false pass may occur when the diagnostic system is unable to identify the presence of a fault that is actually present. False passes may prevent one or more failure mode management actions from being taken to maintain reliable operation. Accurate detection and response to various intermittent faults will reduce false passes.
A diagnostic system may measure the frequency and duration of intermittent faults in order to determine whether the fault may be detrimental to the reliable operation of the control system. If the fault may be detrimental to the reliable operation of the control system, the diagnostic system may take the failure mode management action(s) during an interim period before the DTC is set to protect the control system. The failure mode management action(s) taken during the interim period before the DTC is set may be referred to as temporary default actions as they may be deactivated arbitrarily.
A repeatability of the fault may be determined based on the duration and/or frequency of an intermittent fault. A repeatable intermittent fault, and particularly intermittently occurring critical faults, may be managed similarly to continuous critical faults. When an intermittent fault is repeatable or becomes continuous, the diagnostic system should set the DTC and permanent default action(s) should be taken. Intermittent faults that are repeatable may be repairable because as the likelihood that the root cause can be determined increases. If a fault is not sufficiently repeatable, temporary default action(s) may be removed and normal operation of the control system may be resumed.